Egglaying

Egglaying is the process by which oviparous animals deposit eggs, enabling development to occur outside the female body. It spans a wide range of taxa, including birds, reptiles, fish, monotremes, amphibians, and many invertebrates.

In birds and many reptiles, fertilization occurs internally, and the egg forms in the oviduct, acquiring yolk, albumen, membranes, and a shell. Most birds and many reptiles produce hard-shelled eggs, while some reptiles lay leathery eggs. Monotremes such as the platypus and echidna lay soft, leathery eggs and provide no postnatal nursing via nipples.

In fishes, amphibians, and many invertebrates, eggs are laid in water or nests, with external fertilization common and little or no protective shell. Insects deposit eggs in plant tissue, soil, or onto hosts, depending on the species.

The timing and rate of egglaying vary by species and conditions. Clutch size, laying frequency, and incubation depend on age, season, nutrition, and environment. Incubation temperature and humidity influence hatch success, and parental care ranges from active guarding to none.

Egglaying represents a major reproductive strategy. It enables wide dispersal and, in many species, a degree of parental investment distinct from live birth. In humans and agriculture, eggs from domesticated birds form a key food resource and are a central focus in animal husbandry and developmental biology.